Hydraulic formation packing

ABSTRACT

A WELL AND METHOD OF COMPLETING SAME CHARACTERIZED BY FORCING POROUS PELLETS INTO A NONFRACTURABLE FORMATION OF UNCONSOLIDATED, UNCEMENTED PARTICLES WHICH ARE SUFFICIENTLY MOBILE TO BE COMPACTED OUTWARDLY FROM THE WELL, THUS FORMING AN ARTIFICIAL VOLUME BETWEEN THE WELL BORE AND A NEW ENVELOPE OF COMPACTED PARTICLES, THE VOLUME BEING FILLED WITH THE PELLETS, REPLACING THE ORIGINAL PARTICLES, AND FORMING A PERMEABLE BED THROUGH WHICH FLUID MAY FLOW THROUGH THE ENVELOPE AND PELLET BED TO THE WELL BORE OR CASING IN SAME. SINCE THE AREA OF THE NEW ENVELOPE IS CONSIDERABLY IN EXCESS OF THE ENVELOPE OF THE ORIGINAL UNCOMPACTED PARTICLES, INCREASED FLUID PRODUCTION IS THUS ATTAINED. ALSO, SINCE THE RATE OF MOVEMENT OF FLUID ACROSS THE UNIT AREA OF THE SURROUNDING DRAINAGE ENVELOPE AREA OF THE PELLET BED MAY THUS BE MATERIALLY INCREASED OVER THE ORIGINAL DRAINAGE AREA OF THE PARTICLE BED IMMEDIATELY SURROUNDING THE WELL BORE, THE TENDENCY OF THE FORMATION PARTICLES TO MIGRATE THROUGH THE BED IS REDUCED, THUS REDUCING TENDENCY TO SAND OR CLOG THE CASING OR PUMPING APPARATUS CONTAINED IN SAME.

I United States Patent [111 3,537,741

Inventor Earl Martin Casey Primary Examiner-Stephen J. Novosad Box 110, Powell, Wyo. 82435 Attorney-Sheridan, Ross and Burton 857,673 Sept. 15, 1969 [45] Patented June 28, 1971 ABSTRACT: A well and method of completing same characterized by forcing porous pellets into a nonfracturable formation of unconsolidated, uncemented particles which are sufficiently mobile to be compacted outwardly from the well, thus 6 Chlms,3 Drawing Figs. forming an artificialvolume between the well bore and a new envelope of compacted particles, the volume being filled with the pellets, replacing the original particles, and forming a permeable bed through which fluid may flow through the en- [2 l] Appl. No.

[22] Filed [54] HYDRAULIC FORMATION PACKING reased fluid production is thus attained. Also, since the rate of movea .7 m mawmw at: 4 gglznunuamcflnylvv \ad. o t a 0 0 0 O O 0 o i v o velope and pellet bed to the well bore or casing in same. Since the area of the new envelope is considerably in excess of the envelope of the original uncompacted particles, in

ment of fluid across the unit area of the surrounding drainage envelope area of the pellet bed may thus be materially increased over the original drainage area of the particle bed immediately surrounding the well bore, the tendency of the formation particles to migrate through the bed is reduced, thus reducing tendency to sand or clog the casing or pumping apparatus contained in same.

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INVENTOR EARL M. CASEY ATTORNEYS 1 HYDRAULIC FORMATION PACKING BACKGROUND OF THE INVENTION In certain fluid producing wells, such as oil, gas, and water, but particularly oil, the producing horizon or strata is sometimes found in a soft, nonconsolidated formation which is of a somewhat fluidic nature, consisting partly of liquid or gas and partly of loose or divided particles of the formation. In formations of this type the well may have a relatively short production life since the formation particles tend to follow the flowing fluid being produced and eventually enter the well bore, clogging same against further production. For example, in a pumping well,'the movement of particles of the formation may be such as to sand in the pumping apparatus to the extent that it becomes inoperative and sometimes cannot be removed, ending the productive life of the well.

The problems involved in the sanding of a well have long been appreciated and various methods, such as utilization of screens or like filters, or gravel packing, have been employed to combat sanding. Gravel packing, which is, perhaps, the closest analogy to thepresent invention, is discussed in History of Petroleum Engineering, (1961) published by the American Petroleum Institute, pg. 606 et seq. In this method, and the various other screening or filtering methods, the primary purpose is to prevent entry of sand, silt, or other fines into the well bore which would tend to clog same and either reduce production or prematurely terminate same. The concept in such methods was, accordingly, to maintain a predetermined production rate from a relatively small surrounding drainage area of the producing formation and prevent its particles from migrating into a clogging relation with the well bore, its casing, or its pumping apparatus. It will now become apparent that if a predetermined production rate is assumed, and that by some means this could be increased, the fluid flow rates toward the well would also be increased, tending to produce clogging at an accelerated rate. As will subsequently appear in more detail, the present invention not only provides a method of preventing clogging or sanding, as heretofore, but also prevents it at an increased rate of production. Briefly, then, it could be stated that the present invention provides a method of well completion which not only obviates the sanding problems heretofore encountered but does so with a materially increased production rate which, if attempted heretofore, would have aggravated the sanding problem and materially shortened the useful productive life of the well.

SUMMARY OF THE INVENTION The present invention obviates the foregoing disadvantages and extends the useful life of a well of the type just referred to and also increases its production. It is based upon the general concept that if the formation of compactible particles could be forced outwardly away from the well bore or casing and replaced with other material, such as pellets, which would permit-flow of fluid through same, and also prevent return migration of the outwardly displaced formation particles, the tendency for movement of the formationparticles into the casing would be reduced or eliminated and its production life materially increased. The invention thus provides an artificial bed of pellets with which the casing commuhicates, and a surrounding bed of original formation particles which drain fluid into the artificial bed. Since the surface of the interface between the outer compacted bed and the artificial bed is now materially increased over the interface between the casing and the original formation, as in the prior art, a considerable increase in draining or feeding area of the fluid is attained. Thus, not only is the clogging or sanding problemobviated, but also the production rate of the well is materially increased, the extent of which is dependent upon the volume or envelope surface of the artificial bed. The pellets of the artificial bed may vary; however, in a preferred embodiment they are porous, their pores or passages being filled with soluble material, to prevent clogging of the pores while they are displacing the formation particles, after which the material in the pores is removed to form passages for flow of thefluid to the casing when production is to be started.

The concept has some general analogies to the prior art. For

example, production is increased by providing greater drainage area or volume, as in fracturing, but differs from fracturing in that the particular formation in which the invention is employed is not of a fracturabie nature, and in fact, fracturing of any fracturable formation. adjacent the producing-formation is generally to be avoided since fracturing and propping of an overburden will usually introduce undesired disturbance of the producing horizon. Another analogy is casing screening .or gravel packing to prevent sanding of a casing or its pumping mechanism which is generally confined to a small volume or area immediately surrounding the well bore or casing in same. In this technique, no outward compaction of formation particles is contemplated to form a surrounding artificial porous bed of material size which has forced the original particles outwardly and displaced same. The present invention therefore embodies two old general end results which are: (1) increasing drainage volume and (2) prevention of sanding, but in an entirely different manner than heretofore employed, since it is neither a fracturing technique nor a graveling technique, but it does attain some of the general end results of both. I

The principal object of the invention, accordingly, is to provide a well and method of completing same, of particular utility for use in a fluid producing bed or formation comprising unconsolidated, compactible particles which increases the useful life of the well and increases the production rate of same.

Further objects, advantages, and salient features will become more apparent from the detailed disclosure to follow.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross section of an exemplary well of conventional form and just prior to the completion process of the present invention;

FIG. 2 is a like section during the completion process of the present invention; and

FIG. 3 is a section through a pellet.

Referring now to the drawing, FIG. 1 illustrates a well of the casing through producing formation" type in which a well bore 10 is bored through a hard formation 12, a soft producing formation 14 and terminates in another hard formation 16, disposed below the soft formation. A casing 18 is disposed in the bore and the space between the bore and casing is filled with cement 20 to seal the casing in the various formations. After the cement hardens, perforations 22 are formed in any known manner through the casing and surrounding cement in the locus of producing formation 14. This may be considered as conventional in the art and the well is now ready to produce, such as by installation of a well-known pump within the casing. The soft formation is illustrated as being composed of compactible particles which, for purposes of ease of understanding, may be considered as sand containing the fluid to be produced by the well. As previously referred to, theseparticles tend to flow with the fluid through the perforations and into the casing, clogging same, together with the pumping means (not shown), and shortening or terminating its useful life.

Referring now to FIG. 2, whichillustrates one form of the subject of the invention, pellets P are pumped through the perforations, such as through a pipe 24, sealed to the casing by a packet 26. As these move outwardly, they force the soft formation outwardly and form a pellet bed, surrounding the easing. As illustrated, the soft formation has now been compacted in an outward direction, the closer crosshatching of FIG. 2 illustrating the compaction as compared with the wider hatching of FIG. 1. As will nowbe apparent, an interface 28 between the surrounding area of the pellets and the adjacent compacted area of the soft formation has now been formed, which may be considered as a compacted formation particle envelope surrounding the pellet bed. The pellet bed thus maintains the envelope in a fixed position surrounding same and, due to the porosity of the pellet bed, fluid may drain through same to the casing without migration of the formation particles. As compared with FIG. 1, wherein the envelope of formation particles had a small area equ al substantially to the periphery of the casing times its perforated length, the area of the envelope has now been materially ihcreased, the amount of which is dependent upon the size of the pellet bed. It is also to be observed that since such area is materially increased the rate of flow of fluid across the interface or envelope may be materially decreased thus reducing the tendency of the formation particles to flow or migrate through the pellet bed, tending to clog same. Moreover, while the flow rate per unit area at the interface may be decreased, the overall rate of flow may be materially increased due to the materially increased interface area of FIG. 2 as compared to FIG. 1. Thus, tendency to sand the casing and pump is not only reduced or obviated but the overall rate of production is materially increased.

The pellet bed so far described is to be distinguished from similar pellets employed in the well-known fracturing process. In the latter, pellets are forced under pressure into a hard fracturable formation, forming fissures or cracks in same, usually of a width not to exceed the size of the particles or several diameters or layers of same. The particles then form props for preventing collapse of the fracture, due to the weight of the overburden, and thus provide permeable cracks or fractures in the hard formation and, in effect, tapping a greater volume of the hard formation, increasing its production. in the present invention, the pellets might, in some types of formations, serve as propping agents to some extent, but in general, do not serve such purpose, their principal purpose being to form an artificial porous bed in a compactible formation which replaces a former soft and compactible bed surrounding the well bore. Thus, formation 12, for example, would normally be stable and self supporting without requirement of propping since it was formally supported by compactible material and it may therefore be assumed that its unit pressure on same, due to the overburden was relatively small. It is, moreover, desirable to inject the pellets under pressure which will not produce fracturing in adjacent hard fracturable formations and thus create a change in same which would cause fracturing and any tendency to collapse due to the overburden.

The pellets may be formed of various materials, shapes and sizes which may be pumped with a fluid, as in the fracturing process. In an exemplary form, however, as illustrated in FIG. 3, they may be generally spherical pellets having channels 30 extending through same and/or surface grooves or channels 32, the channels being filled with removable material 34. The material serves a dual purpose in that it prevents movement of the formation particles into the pellet grooves and channels, tending to clog same, during the outward compaction of the formation particles and permits its removal when it is desired to place the well in production. Limestone, for example, may be employed to fill the channels and interstices which may be removed by injecting a suitable acid (such as HCl or H 50 into the pellet bed when it is desired to increase its porosity and commence production of the well. Other filler materials may of course be employed, depending upon the type of well.

For example, if it is to produce water, then a water soluble material, such as common salt may be employed. The size of the particles may vary between minute and of the order of one-half inch diameter for perforated casings and, for open hole" completions (where the casing is not perforated), up to several inches in diameter.

Open hole completions, just referredto, (not illustrated) are similar to FIG. 2 but differ in that the lower open end of the casing terminates at the soft formation, rather than passing through same and into a subterranean hard fonnation. The casing may be cemented in above the soft formation but its lower open end forms the fluid conduit to the formation, rather than perforations in its wall. As will be apparent, when the casing terminates above the lower surface of the formation, rather than passing through same, the soft formation may be compacted downwardly beyond the lower end of the casing as well as in radially outward directions, thus in some instances, depending upon the formation, producing a pellet bed of a volume greater than the casing-through type.

The term well completion" as hereinafter employed in the claims is intended in its broader sense to also include f cgmpletion. Thus, if the well has previously been in production andits production rate is not considered sufficient or has become uneconomical, the well may be modified in accordance with the same methods employed in an original completion.

I claim:

l. A completion method for a well for increasing its production and preventing sanding of same, the well bore communicating with a stratum bed of nonconsolidated particles which tend to migrate toward the well bore with the fluid contained therein, said stratum bed not being subject to fracturing, comprising the steps of:

a. replacing the particles contained within a volume of said stratum bed in a locus between the well bore and an envelope interface outwardly thereof with an artificial bed of porous pellets having channels therewithin of a size through which fluid may flow but which prevent flow of said particles therethrough; and I b. permitting fluid to flow across the envelope interface and through the pellet bed toward the well bore.

2. A method in accordance with claim 1 including the prior steps of forming the pellets with pores filled with removable solid material, and removing said material, after the pellet bed is formed, increasing the permeability of same.

3. A method in accordance with claim 2 wherein said material is such that it may be placed into solution with a liquid.

4. A method in accordance with claim 3 wherein said material is limestone and said liquid is an acid reactable with the limestone to form a compound in liquid form.

5. A method in accordance with claim 3 wherein said material is salt and said liquid is water.

6. A method in accordance with claim 1 wherein said volume is formed by forcing the pellets into the stratum bed, compacting the particles ahead thereof in a direction away from the well bore. 

